Acidic Cerium Research Articles

Determination of Remifentanil in Pharmaceuticals Using Chemiluminescence System of Ru(phen)32+-Ce(IV)

In this study, new chemiluminescence (CL) method was proposed to determine the amount of remifentanil in pharmaceuticals. We found that the weak CL intensity in the reaction between acidic cerium(IV) and Ru(phen)32+ complex increases significantly in the presence of remifentanil. Effect of remifentanil was investigated in some other CL systems such as luminol-IO4-, direct oxidation using acidic cerium(IV) or acidic KMnO4. Moreover, the effect of different dyes as a sensitizer was investigated in the KMnO4-Dye CL system. The dyes used in this study were crystal violet, amido black, naphthol green, amaranth, rhodamine 6G, safranin, orange G, fluorescein, and chromotrope 2R. The results showed that remifentanil has the highest CL intensity and S/B ratio in the acidic cerium(IV)- Ru(phen)32+ CL system. The reaction mechanism was evaluated by studying the CL reaction kinetics in the presence and absence of remifentanil and spectrophotometric spectra. The results indicate that remifentanil can convert Ru(phen)33+ complex rapidly to Ru(phen)32+* complex, which emits light when it returns to its ground-state. The method's linear dynamic range, detection limit, and reproducibility for four repetitive measurements of 109.39 μg mL-1 were 1.75-145.85, 1.41 μg mL-1, and 2.3%, respectively. The method proposed in this study was used to determine the content of remifentanil in pharmaceutical preparations.

Exploitation the unique acidity of novel cerium-tungstate catalysts in the preparation of indole derivatives under eco-friendly acid catalyzed Fischer indole reaction protocol

Solid acidic cerium tungstate catalysts containing different molar ratios of cerium and tungstate were prepared by direct solvothermal methodology. The structure of the prepared catalysts was deeply studied and confirmed based on different characterization techniques such as DTA-TGA, FTIR, Raman spectra, XRD and N 2 adsorption measurements. Moreover, FTIR and TPD of chemically adsorbed pyridine techniques were conducted to fully address the nature and the strength of the acidic sites of the prepared catalysts. The study showed that at a lower molar ratio of tungstate, the catalyst contains cerium oxide phase and slight participation of cerium tungstate phase, which gradually increases with further increase of tungstate molar ratio. This phase change was also accompanied by a noticeable change in the thermal stability, surface area and acidic properties of the prepared catalysts. Additionally, the techniques used to study the acidic properties showed an excellent enhancement in the acidic centers. It was also noted that the strength of these acidic centers reached the maximum in the case of using tungstate: cerium molar ratio 2:1 (CeW2.0) catalyst, and slightly decreased thereafter. By exploiting the acidic properties of the prepared catalysts, a series of indole derivatives were synthesized via the Fischer indole synthesis strategy. The results also showed that ∼100% of indole derivatives were obtained using 0.02 g catalyst at 80 °C after 2 h only. Moreover, the Reuse experiment demonstrated the possibility of recycling and reusing the catalyst through many cycles with high efficiency, indicating its wonderful constancy and reusability.

A comprehensive evaluation of three microfluidic chemiluminescence methods for the determination of the total phenolic contents in fruit juices

Three recently reported microfluidic chemiluminescence (MF-CL) methods (based on reactions with acidic permanganate enhanced by formaldehyde (KMnO4-COH), acidic cerium (IV) and rhodamine B (Ce-RB), and acidic cerium (IV) and rhodamine 6G (Ce-R6G) enhanced by SDS) for the determination of the total phenolic content (TPC) in juices were critically evaluated in terms of their selectivity. The evaluation was carried out using 86 analytes, including 22 phenolic compounds (phenolic acids and polyphenols), 6 known non-phenolic antioxidants, 9 amino acids and a number of proteins, carbohydrates, nucleotide bases, inorganic salts and other compounds. Each method was sensitive toward phenolic compounds (PCs). However, the KMnO4-COH CL system showed a higher sensitivity toward phenolic acids and also responded to non-phenolic antioxidants. The other two systems showed higher sensitivity toward polyphenolic compounds than to phenolic acids and did not responded to all other compounds including non-phenolic antioxidants.

Flow‐injection chemiluminescence and electrogenerated chemiluminescence determination of escitalopram oxalate in tablet form

Rapid, simple and highly sensitive flow-injection (FI) chemiluminescence (CL) and flow-injection electrogenerated chemiluminescence (ECL) methods were developed for the determination of escitalopram oxalate (ESC), a selective serotonin reuptake inhibitor used as an antidepressant drug. The CL method was based on the CL reaction of ESC with acidic cerium(IV) and tris(2,2'-bipyridyl)ruthenium(II) (Ru(bipy)(3)(2)+). Various experimental parameters affecting CL intensity were carefully studied and optimised. The method enabled the determination of 0.001-50 µg/mL of ESC in bulk form with a correlation coefficient r = 0.9999. The limit of detection (LOD) was 0.01 ng/mL (S/N = 3). The ECL method was based on the ECL reaction of Ru(bipy)(3)(2)+ with the drug in an acidic medium, permitting the determination of ESC in the range of 0.00001-70 µg/mL with r = 0.9999 and LOD of 1 x 10(-4) ng/mL. The proposed methods were applied to the determination of ESC in commercial tablets. The results were compared statistically with those obtained from a published method using t- and F-tests.

Flow injection determination of benzhexol based on its sensitizing effect on the chemiluminescent reaction of Ce(IV)–sulfite

In this paper, a novel chemiluminescent (CL) method for the determination of benzhexol has been developed by combining the flow injection technique and its sensitizing effect on the weak CL reaction between sulfite and acidic cerium(IV). A mechanism for the CL reaction has been proposed on the basis of CL spectra. Under the optimized conditions, the proposed method allows the measurement of benzhexol hydrochloride over the range 0.1-10 microg/mL with a correlation coefficient of 0.9992 (n = 8), a detection limit of 0.02 microg/mL (3sigma), and a relative standard deviation for 2.0 microg/mL benzhexol (n = 11) of 1.65%. The utility of this method was demonstrated by determining benzhexol hydrochloride in tablets.

Chemiluminescence mechanisms of cerium-norfloxacin and its application in urine analysis

AbstractIn this article, novel chemiluminescence mechanisms between norfloxacin and cerium(IV) in an acidic medium were studied. Chemiluminescence spectra of the present system were recorded observing three maximum emissions at about 475 nm, 550 nm, and 620 nm, respectively. The results indicate that the chemiluminescence peaks located at 475 nm and 620 nm can be ascribed to the emission of a singlet oxygen, while the chemiluminescence emission at 550 nm occurred in course of the reaction between acidic cerium(IV) and the phenolic intermediate. Under optimum conditions, the chemiluminescence intensity was linear with the concentration of norfloxacin over the range of 2.0 × 10−8−1.0 × 10−5 g mL−1 and the detection limit of 1.0 × 10−8 g mL−1 (S/N = 3). The relative standard deviation was 1.94 % for a 4.0 × 10−7 g mL−1 norfloxacin solution considering eleven repeated measurements. The present chemiluminescence system was successfully applied in the determination of norfloxacin in pharmaceutical preparations and concentration-time profiles in urine.

Selectivity and potential interference from phenolic compounds in chemiluminescence methods for the determination of synephrine

Three recently reported chemiluminescence methods (based on reactions with alkaline luminol and hexacyanoferrate(III); acidic cerium(IV) and rhodamine B; and acidic permanganate with polyphosphates) for the determination of synephrine were re-evaluated in terms of their selectivity towards this analyte in comparison to other phenolic compounds. A fourth reagent system, acidic soluble manganese(IV) and formaldehyde, was also examined. Each set of reagents was sensitive towards synephrine (limits of detection were 3 x 10(-9), 5 x 10(-8), 1 x 10(-8) and 1 x 10(-8) mol/L, respectively) but also responded with numerous other phenolic compounds, including some that are present in citrus fruit extracts, dietary supplements and/or biological fluids. It is therefore recommended that the determination of synephrine in these matrices should incorporate physical separation of sample components (e.g. chromatography or electrophoresis). In more general terms, this study illustrates that accurate percentage recoveries for an analyte in spiked samples (without validation against another analytical method) are insufficient to confirm the analytical utility of new flow-injection analysis (FIA) procedures.

Chemiluminescence method for the determination of mitoxantrone by the enhancement of the tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II)–cerium(IV) system

A new injection chemiluminescence system was used for the determination of mitoxantrone. The technique is based on the reduction effect of mitoxantrone on the tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II), which is produced by reaction between tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II) and acidic cerium(IV) solutions, and this rapid reduction produces strong chemiluminescence. The chemiluminescence intensity was so high that it is able to produce a detection limit of 1.4 × 10−8 mol L−1 mitoxantrone (3σ). The relative standard deviation of 1.0 × 10−6 mol L−1 mitoxantrone was 1.9% (n = 11). The method was successfully applied to the determination of mitoxantrone in pharmaceutical preparations in capsule, spiked serum and urine samples.

Sensitive Monitoring of Humic Acid in Various Aquatic Environments with Acidic Cerium Chemiluminescence Detection

In this research, a simple, sensitive chemiluminescence (CL) method for the determination of humic acid (HA) in water samples was first developed based on the redox reaction between humic acid and cerium(IV) in the acidic condition. Different with the former redox CL reaction which occurred in alkaline solution, no enhancers were needed and neither precipitation nor a second contamination would occur in the present CL system. Comparing with other spectrometric methods, we find that the proposed analysis system had better applicability and accuracy. Under the optimal experiment conditions, the CL peak height was linear with the concentration of HA in the range of 0.03 to 10.0 microg mL(-1). The detection limit is 0.01 microg mL(-1) (S/N = 3), and the relative standard deviation was 2.3% for 0.5 microg mL(-1) HA solution with eleven repeated measurements. The present CL method was successfully applied to the determination of HA in tap water, spring water and river water samples with good recovery from 90.0 to 110.0%. A possible CL mechanism was proposed based on the results of UV and fluorescence spectrometry and the CL spectrum of HA. It was speculated that the semi-quinone radicals in the excited state were the emitters.

On‐line chemical generation of tris(2,2′‐bipyridyl)ruthenium(III) and its application in CE with chemiluminescence detection

A novel tris(2,2'-bipyridyl)ruthenium(III) [Ru(bipy)(3) (3+)]-based chemiluminescence (CL) detection in CE using an on-line chemical generation scheme has been demonstrated. Two continuous streams respectively containing solutions of Ru(bipy)(3) (2+) and acidic cerium(IV) used as a homogeneous chemical oxidant are employed to generate Ru(bipy)(3) (3+), which is delivered into the reaction capillary of a coaxial flow interface and then reacted with analytes at the end of the separation capillary to yield light. The important operational parameters for separation and detection are identified and optimized. Four alpha-ketocarboxylic acids used as models, outside of the amine-containing compounds, are successfully separated and detected to evaluate the feasibility of the approach. The excellent resolution and detection sensitivity was achieved by using 50 mmol/L phosphate running buffer (pH 9.5) with 0.7 mmol/L CTAB, and CL reagent solution streams containing 0.15 mmol/L Ru(bipy)(3) (2+) and 0.8 mmol/L cerium(IV) (0.25 mol/L H(2)SO(4)), respectively. The concentration detection limits for alpha-ketocarboxylic acids were below 3.7x10(-8) mol/L (S/N = 3). The proposed method was applied to the determination of alpha-ketocarboxylic acids in five different honey samples with satisfactory results.

Macrolactamization of Glycosylated Peptide Thioesters by the Thioesterase Domain of Tyrocidine Synthetase

The 35 kDa thioesterase (TE) domain excised from the megadalton tyrocidine synthetase (Tyc Syn) retains autonomous capacity to macrocyclize peptidyl thioesters to D-Phe1-L-Leu10-macrolactams. Since a number of nonribosomal peptides undergo O-glycosylation events during tailoring to gain biological activity, the Tyc Syn TE domain was evaluated for cyclization capacity with glycosylated peptidyl-S-NAC substrates. First, Tyr7 was replaced with Tyr(beta-D-Gal) and Tyr(beta-D-Glc) as well as with Ser-containing beta-linked D-Gal, D-Glc, D-GlcNAc, and D-GlcNH2, and these new analogs were shown to be cyclized with comparable kcat/Km catalytic efficiency. Similarly, Gal- or tetra-O-acetyl-Gal-Ser could also be substituted at residues 5, 6, and 8 in the linear decapeptidyl-S-NAC sequences and cyclized without substantial loss in catalytic efficiency by Tyc Syn TE. The cyclic glycopeptides retained antibiotic activity as membrane perturbants in MIC assays, opening the possibility for library construction of cyclic glycopeptides by enzymatic macrocyclization.

Flow‐Injection Chemiluminescence Determination of Papaverine Using Cerium(IV)‐Sulfite System

ABSTRACT A sensitizing effect of papaverine on the weak chemiluminescence (CL) reaction of sulfite with acidic cerium(IV) is studied. In papaverine and cerium(IV) solution, the increase in the fluorescent intensity of cerium(III) at 360 nm with an increasing time indicates a slow oxidation of papaverine by acidic cerium(IV). This reaction results in the formation of intermediate radical of papaverine, which enhanced the CL emission of sulfite–cerium(IV) system. Based on this finding, a flow injection (CL) method is proposed for the determination of papaverine. The CL intensity is proportional to the concentration of papaverine from 1.0 × 10−7 to 1.0 × 10−5 M with a correlation coefficient of 0.9991. The detection limit is 8.7 × 10−8 M (3σ). The relative standard deviation for seven independent determinations of 1.0 × 10−6 M papaverine is 2.0%. The proposed method has been satisfactorily used for the determination of papaverine in pharmaceutical preparations and biological fluids.

Determination of flufenamic acid and mefenamic acid in pharmaceutical preparations and biological fluids using flow injection analysis with tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection

A novel chemiluminescent method using flow injection has been investigated for the rapid and sensitive determination of flufenamic and mefenamic acids. The method is based on a tris(2,2′-bipyridyl)ruthenium(III) chemiluminescence reaction. Ru(bipy) 3 3+ is chemically generated by mixing two streams containing solutions of tris(2,2′-bipyridyl)ruthenium(II) and acidic cerium(IV) sulphate. After selecting the best operating parameters calibration graphs were obtained over the concentration ranges 0.07–6.0 and 0.05–6.0 μg ml −1 for flufenamic acid and mefenamic acid, respectively. The limits of detection ( s/ n=3) were 3.6×10 −9 M flufenamic acid and 2.1×10 −7 M mefenamic acid. The method was successfully applied to the determination of these compounds in pharmaceutical formulations and biological fluids. A proposal for the reaction pathway was given.

Improvement of the tetrachloromercurate absorption technique for measuring low atmospheric SO2 mixing ratios

During the Gas‐Phase Sulfur Intercomparison Experiment (GASIE) in 1994 an analytical system for measuring sulfur dioxide mixing ratios at low parts per trillion (pptv) levels was employed. It is based on the absorption of SO2 on a tetrachloromercurate(II)‐impregnated filter. The subsequent analysis uses a chemiluminescence reaction by treating the resulting disulfitomercurate(II) complex with an acidic cerium sulfate solution. An improved sampling device has been introduced that increases the maximum sampling volume from 200 L to 500 L. It is also possible to determine the blank value accurately for each sample. The absorption efficiency of the sampling system is 98.7±6.4% at a nominal flow rate of 10 L/min. The calculated (3σ) detection limit is 3±1 pptv SO2. The sample solution is stable for up to 30 days, which allows the samples to be safely stored or shipped before analysis. This permits the use of a sensitive, compact, and reliable sampling system in the field with subsequent analysis under optimal conditions in the laboratory. A continuous flow chemiluminescence (CFCL) analyzer for on‐line measurements is also presented. The system is based on the same chemical principles as the described filter technique.